1,2-Propanediol Process with Tungstate Extraction and Recycle
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Solution Overview
Problem
The existing process for producing 1,2-propanediol results in significant losses of tungstate in the aqueous phase, which are either lost or require costly recovery from bottoms products during distillation.
Innovation Solution
A method involving the use of an extractant solution with a phase transfer catalyst and solvent to separate and recycle the aqueous phase, allowing for the recovery of heteropolytungstate and phase transfer catalyst, thereby reducing losses and optimizing the process efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If distillation is used to recover 1,2-propanediol from the aqueous phase, then product recovery is achieved, but tungstate is lost in the residual bottoms product
Solution Approach 1:
The patent extracts tungstate from the aqueous phase before distillation by adding an extractant solution. The extractant selectively transfers tungstate into an organic extract phase, separating it from the aqueous phase containing 1,2-propanediol. This prevents tungstate from being lost in the distillation bottoms while allowing complete recovery of the diol product.
Solution Approach 2:
The patent segments the recovery process into distinct stages: first extracting tungstate into a separate organic phase, then performing distillation on the depleted aqueous phase. This segmentation allows independent optimization of each step - tungstate recovery through extraction and diol recovery through distillation - eliminating the trade-off between product recovery and catalyst retention.
2Loss of substance
If tungstate recovery from bottoms product is implemented, then catalyst loss is reduced, but process complexity and cost increase
Solution Approach 1:
The patent performs tungstate extraction as a preliminary step before distillation. By removing tungstate from the aqueous phase in advance, the subsequent distillation process becomes simpler and does not require complex bottoms product treatment systems. The extractant is easily separated and recycled, reducing overall process complexity compared to post-distillation recovery methods.
Solution Approach 2:
The extractant acts as an intermediary substance that facilitates tungstate transfer from the aqueous phase to an organic phase. This intermediary enables selective separation without requiring complex equipment - simply mixing and phase separation. The extractant can be readily recycled back into the reaction system, creating a simple closed loop that reduces both equipment and operational complexity.
3Productivity
If phase transfer catalyst and solvent are used in oxidation reaction, then reaction efficiency is improved, but tungstate loss in aqueous phase increases
Solution Approach 1:
The patent deliberately discards tungstate from the aqueous phase through extraction with an extractant solution, then recovers it in the organic extract phase. The extracted tungstate-containing organic phase is recycled back to the oxidation reactor. This approach maintains high reaction efficiency by preserving the phase transfer catalyst system while preventing tungstate loss through systematic recovery and recycling.
Solution Approach 2:
The patent implements a feedback loop where the extractant phase, enriched with tungstate after extraction, is recycled back to the oxidation reaction system. This feedback ensures continuous replenishment of tungstate catalyst in the reaction zone, maintaining high oxidation efficiency while the extraction step continuously removes tungstate from the aqueous phase to prevent its loss in distillation bottoms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces tungstate losses and enhances the economic viability by recycling valuable catalyst components, facilitating a more resource-efficient and cost-effective production of 1,2-propanediol.
Implementation Method 1
extracting the separated aqueous phase (Pa) with an extractant solution comprising the same phase transfer catalyst and the same solvent (S) as used in step a) to provide an extracted aqueous phase (Pae) and an extract phase (Pe)
Implementation Method 2
separating the liquid reaction mixture of step a) into an aqueous phase (Pa) comprising 1,2-propanediol and an organic phase (Po)
Data Source
AI summary
A method for preparing 1,2-propanediol involves reacting propene with hydrogen peroxide, in the presence of a phase transfer catalyst and a heteropolytungstate, in a liquid reaction mixture containing an aqueous phase with a maximum apparent pH of 6 and an organic phase containing a solvent having a solubility in water at 20° C. of less than 500 mg/kg. The method then involves separating the liquid reaction mixture into an aqueous phase containing 1,2-propanediol and an organic phase; recycling at least a part of the separated organic phase to the reaction; and extracting the separated aqueous phase with an extractant solution containing the same phase transfer catalyst and solvent as used in the reaction to provide an extracted aqueous phase and an extract phase. The method further involves recycling at least a part of the extract phase to the reaction and recovering 1,2-propanediol from the extracted aqueous phase.